Required Practical 3: Resistance

• What is the focus of the practical described in the video?

  Factors affecting the resistance of electrical circuits
• What percentage of exam marks come from required practicals?

  At least 15%
• What equipment is used in the resistance practical?

  Battery, ammeter, voltmeter, wire
• What does the ammeter measure in the circuit?

  Current
• What does the voltmeter measure in the circuit?

  Potential difference across the wire
• How do you calculate resistance in the circuit?

  Resistance = Potential difference / Current
• What factor are we investigating that affects resistance?

  Length of the wire
• How can you increase the length of the wire in the circuit?

  Move the crocodile clips further apart
• What does a straight line graph through zero indicate?

  Resistance is directly proportional to length
• What is a zero error?


  Reading when the value should be zero
• Why is zero error considered a systematic error?

  It cannot be reduced by repeating measurements
• How should you adjust readings to account for zero error?

  Subtract zero error from all readings
• What causes zero error in this experiment?

  Contact resistance and positioning of clips
• How does temperature affect resistance?

  Increased temperature raises resistance
• What can be done to reduce heating effects in the wire?

  Use low potential difference and turn off current
• What is a variable resistor used for?

  To control the potential difference across a component
• How does a variable resistor change resistance?

  By changing the length of the wire in a coil
• What happens to a lamp when resistance is increased?

  The lamp becomes dimmer
• What are the steps to investigate resistance in a circuit?

  1. Set up the circuit with battery, ammeter, voltmeter, and wire.
  2. Measure current and potential difference.
  3. Calculate resistance using $R =$$\frac{V}{I}$.
  4. Change the length of the wire using crocodile clips.
  5. Record readings and plot a graph.
• What are the key issues to consider in the resistance practical?

  • Zero error: systematic error affecting readings
  • Heating effects: increase in resistance with temperature
  • Use low potential difference to minimize heating
  • Turn off current between readings to reduce heating